1. Field of the Invention
The present invention relates to an optical pickup for performing at least the action of either optically recording or reproducing the data on different types of information recording mediums such as optical discs and the like, an optical disc apparatus equipped with the optical pickup, an optical information equipment equipped with the optical disc apparatus, and an integrated coupling lens and an integrated prism installed in the optical pickup.
2. Description of the Related Art
As blue-violet semiconductor laser diodes have been introduced for practical use, Blu-ray Discs (referred to as BDs hereinafter) of high-density, mass-storage optical information recording mediums (referred to as optical disc hereinafter) are now put to practical use which are identical in the size to CDs (compact discs) and DVDs (digital versatile discs). The BDs are optical discs on which data are recorded or played back with the use of a blue-violet laser source which emits a blue-violet laser beam. Also, HD-DVDs are put to practical use on the basis of a blue-violet laser source. The expression “either recording or playing back” in this specification means that at least either the recording action or the playback action is to be performed.
The CDs are optical discs in which the thickness of their transparent substrate from the optical disc surface to the information recording surface is 1.2 mm, the wavelength of laser beam for performing either the recording or playback is substantially 780 nm, the numerical aperture NA of their objective lens ranges from 0.45 to 0.55, and their recording capacity is substantially 650 MBytes.
It is required for performing either the recording action or the playback action at higher densities on the optical discs to minimize the diameter of the spot of the laser beam focused by the objective lens. To minimize the diameter of the spot of the laser beam, the wavelength λ has to be shortened while the numerical aperture NA of the objective lens is increased.
However, when the numerical aperture NA of the objective lens is increased, in proportion to the cube of the NA, the comatic aberration derived from tilting of the transparent substrate becomes large. As the comatic aberration is proportional to the thickness of the transparent substrate, it can be suppressed by thinning the transparent substrate.
The DVDs are optical discs in which the thickness of their transparent substrate is 0.6 mm, the wavelength of laser beam for performing either the recording or playback action is substantially 650 nm, the numerical aperture NA of their objective lens ranges from 0.60 to 0.65, and their recording capacity at one layer is substantially 4.7 GBytes. The DVD is made of two 0.6 mm thick discs bonded to each other and its total thickness is thus 1.2 mm as equal to that of a CD.
The BDs are optical discs in which the thickness of their transparent substrate is about 0.1 mm, the wavelength of laser beam for performing either the recording or playback action is substantially 405 nm, the numerical aperture NA of their objective lens is 0.85, and their recording capacity at one layer is substantially 25 GBytes. The BD has a recording layer provided on a disc base material of 1.1 mm thick and protected with a transparent cover layer of 0.1 mm thick (the transparent substrate) and its total thickness is thus 1.2 mm as equal to that of a CD. Either the recording action or the playback action on the recording layer is performed with a laser beam converged from the transparent cover layer to the recording layer. An increase of the comatic aberration produced by a combination of the laser beam at shorter wavelengths and the objective lens at higher NA is suppressed by thinning the transparent cover layer through which the laser beam passes to substantially 0.1 mm.
The HD-DVDs are optical discs in which the wavelength of laser beam for performing either the recording or playback action is substantially 405 nm, the numerical aperture NA of their objective lens is 0.65, and their recording capacity at one layer is substantially 15 GBytes. The HD-DVD like the DVD is made of two 0.6 mm thick discs bonded to each other and its total thickness is 1.2 mm as equal to that of a CD.
As explained, there are available such different types, CD, DVD, BD, and HD-DVD, of the optical discs. Accordingly, some optical pickups of compatible type have been proposed for performing either the recording action or the playback action with the use of three different wavelengths of the laser beams focused by a plurality of objective lenses to scan the different types of the optical discs.
For example, disclosed in Japanese Patent Laid-open Publication No. 2006-147075, is an optical pickup arranged compatible with four different types, CD, DVD, BD, and HD-DVD, of the optical discs by switching the combination of two objective lenses and light sources.
In an optical pickup 150 illustrated in FIG. 69 is an optical disc 101 of four different standards of optical discs, BD 101a, HD-DVD 101b, DVD 101c, and CD 101d. 
A blue-violet laser beam with an oval shape of intensity distribution emitted from the light source 102 is converted into a beam substantially a circular shape of the intensity distribution by a beam shaping part 103. The laser beam released from the beam shaping part 103 is then directed to a diffraction grating 104 where diffracted light components are produced for controlling the tracking action with a differential push pull (DPP) technique, passed through a polarizing beam splitter 105, and converted into a collimated light beam by a collimator lens 106. Then part of the laser beam released from the beam shaping part 103 is entered into a monitor optical detector 108 by a dichroic mirror 107.
The laser beam passed through the dichroic mirror 107 is passed through a spherical aberration compensating system 109. The spherical aberration compensating system 109 has a function of compensating the spherical aberration caused by a variation in the thickness of the transparent substrate of the optical disc of particularly the BD standard. The laser beam released from the spherical aberration compensating system 109 is bent to substantially 90 degrees in the optical axis by a riser mirror 110 and then passed through a ¼ waveplate 111a or 111b. The laser beam passed through the ¼ waveplate 111a is focused by an objective lens 112a to form its spot on the information recording surface of a BD 101a. The laser beam passed through the ¼ waveplate 111b is focused by an objective lens 112b to form its spot on the information recording surface of an HD-DVD 101b. 
For ease of the description, the optical axis shown in FIG. 69 is turned through 90 degrees in relation to the paper surface between the spherical aberration compensating system 109 and the riser mirror 110.
The ¼ waveplates 111a, 111b and the objective lenses 112a, 112b are mounted on and driven together by an actuator 114 in order to follow surface undulations and data track eccentricities of any of the optical discs 101a to 101d. Also, the objective lenses 112a and 112b disposed on the actuator 114 for performing either the recording action or the playback action can be switched from one to the other by turning an objective lenses mount about its optical axis for scanning the BD 101a or the HD-DVD 101b. 
The laser beam reflected by the BD 101a or the HD-DVD 101b is passed back through the objective lens 112a or 112b and received by the ¼ waveplate 111a or 111b where it is shifted to a linearly polarized light which is different from that at the advancing path. The laser beam is further passed through the riser mirror 110, the spherical aberration compensating system 109, the dichroic mirror 107, and the collimator lens 106 before reflected by the polarizing beam splitter 105. The laser beam reflected by the polarizing beam splitter 105 is projected on an optical detector 116 by a detecting part 115. The optical detector 116 is provided for detecting the focusing error signal, the tracking error signal, and the data signals recorded on the BD 101a or the HD-DVD 101b. 
The recording action and the playback action on the DVD 101c will now be described. A red laser beam emitted from a light source 117 is passed through a diffraction grating 118, reflected by a dichroic beam splitter 119 and a polarizing mirror 120, and converted into a collimated light beam by a collimator lens 121. The laser beam released from the collimator lens 121 is passed through a dichroic mirror 107 and then is partially received by a monitor optical detector 108.
The laser beam reflected by the dichroic mirror 107 is further passed through the spherical aberration compensating system 109, the riser mirror 110, and the ¼ waveplate 111a and focused by the objective lens 112a to form its spot on the DVD 101c. 
The reflection of the laser beam from the DVD 101c is passed back through the objective lens 112a and received by the ¼ waveplate 111a where it is shifted to a linearly polarized mode which is different from that at the advancing path. The laser beam at its polarized mode is passed through the riser mirror 110, the spherical aberration compensating system 109, the dichroic mirror 107, and the collimator lens 121 before received by the polarizing mirror 120. The laser beam passed through the polarizing mirror 120 is projected on an optical detector 123 by a detector lens 122. The optical detector 123 is provided for detecting the focusing error signal, the tracking error signal, and the data signals recorded on the DVD 101c. 
The recording action and the playback action on the CD 101d will now be described. An infrared laser beam emitted from a light source 124 is passed through a diffraction grating 125 and the dichroic beam splitter 119, reflected by the polarizing mirror 120, and converted into a collimated light beam by the collimator lens 121. The laser beam released from the collimator lens 121 is passed through the dichroic mirror 107 and then partially received by the monitor optical detector 108.
The laser beam reflected by the dichroic mirror 107 is further passed through the spherical aberration compensating system 109, the riser mirror 110, and the ¼ waveplate 111b and focused by the objective lens 112b to form its spot on the CD 101d. 
The laser beam reflected on the CD 101d is passed back through the objective lens 112b and received by the ¼ waveplate 111b where it is shifted to a linearly polarized mode which is different from that at the advancing path. The laser beam at its polarized mode is passed through the riser mirror 110, the spherical aberration compensating system 109, the dichroic mirror 107, and the collimator lens 121 before received by the polarizing mirror 120.
The laser beam passed through the polarizing mirror 120 is projected on the optical detector 123 by the detector lens 122. The optical detector 123 is provided for detecting the focusing error signal, the tracking error signal, and the data signals recorded on the CD 101d. 
The first objective lens 112a is of a compatible type for use with both the BD 101a and the DVD 101c. For performing the recording action or the playback action on the BD 101a, the light source 102 is activated for emitting a blue-violet laser beam through transmission across its transparent substrate of about 0.1 mm thick and convergence at the numerical aperture NA of 0.85. For performing the recording action or the playback action on the DVD 101c, the light source 117 is activated for emitting a red laser beam through transmission across its transparent substrate of about 0.6 mm thick and convergence at the numerical aperture NA of 0.6 to 0.65.
The second objective lens 112b is of a compatible type for use with both the HD-DVD 101b and the CD 101d. For performing the recording action or the playback action on the HD-DVD 101b, the light source 102 is activated for emitting a blue-violet laser beam through transmission across its transparent substrate of about 0.6 mm thick and convergence at the numerical aperture NA of 0.65. For performing the recording action or the playback action on the CD 101d, the light source 124 is activated for emitting an infrared laser beam through transmission across its transparent substrate of about 1.2 mm thick and convergence at the numerical aperture NA of 0.45 to 0.55.
As described, the conventional optical pickup 150 of the compatible type where the objective lenses are switched from one to the other is capable of performing either the recording action or the playback action on any of the four different types, CD, DVD, BD, and HD-DVD, of the optical discs.
Further, other apparatuses arranged compatible with different types of the optical disc by optically switching the optical path of laser beam emitted from a single light source are disclosed in Japanese Patent Laid-open Publication No. 2001-344803 and Japanese Patent Laid-open Publication No. 11-120606. For example, disclosed in Japanese Patent Laid-open Publication No. 2001-344803 is an optical pickup for selectively switching the optical path of laser beam with the use of a polarization converter and a polarizing beam splitter.
An optical pickup 250 is illustrated in FIG. 70 where a blue-violet laser beam emitted from a first light source 201 is converted into a collimated light beam by a collimator lens 202. The collimated laser beam is passed through a polarization converter 203. When the laser beam emitted from the light source 201 is of polarized laser beam A (of which the direction of polarization extends upwardly and downwardly in the drawing), it directly passes through the polarization converter 203 which remains not in action. The polarized laser beam A of the laser beam is then passed through a dichroic mirror 205 and received by a polarizing beam splitter 213. The polarized laser beam A of the laser beam passed through the polarizing beam splitter 213 is converted into a circularly polarized laser beam By a ¼ waveplate 212 and then focused by a first objective lens 211 to form its spot on the information recording surface of an optical disc corresponding to the first optical lens 211.
The laser beam is reflected by the information recording surface, passed through the first objective lens 211, and converted into a polarized laser beam B by the ¼ waveplate 212. The polarized laser beam B is reflected by the polarizing beam splitter 213 and projected on an optical detector 215 by a detecting part 214.
The polarization converter 203 in the optical pickup 250 plays an important role. The polarization converter 203 may be implemented by a liquid crystal device or a transparent piezoelectric device. An example is shown in FIG. 71 where the polarization converter 203 is implemented by a liquid crystal device which lines up in a direction denoted by OD with respect to the optical axis. With its electrodes 208, shown in FIG. 71, loaded with a voltage, the polarization converter 203 converts the laser beam from the polarized laser beam A to a polarized laser beam B. With its electrodes 208 remaining loaded with no voltage, the polarization converter 203 passes the polarized laser beam A without changing the direction of polarization. When the polarization converter 203 is in action, it converts the laser beam to the polarized laser beam B (of which the direction of polarization extends vertical to the paper surface in the drawing) which is turned through 90 degrees in the direction of polarization from the incident beam. This allows the laser beam to be reflected by the polarizing beam splitter 213, converted into a circularly polarized laser beam By the ¼ waveplate 210, and focused by a second objective lens 209 to form its spot on the information recording surface of an optical disc corresponding to the second objective lens 209.
The laser beam reflected on the information recording surface of the optical disc is passed through the second objective lens 209, and converted back to the polarized laser beam A by the ¼ waveform plate 210. The polarized laser beam A is then passed through the polarizing beam splitter 213 and projected on the optical detector 215 by the detecting part 214.
As described, the laser beam at the polarized laser beam A is converted by the polarization converter 203 into the polarized laser beam B of which the direction of polarization extends at a right angle to that of the polarized laser beam A. By switching its light path with the polarizing beam splitter 213 and selecting the objective lens to be used, the laser beam can be operable with two different types, BD and HD-DVD for example, of the optical discs which are identical in the light source wavelength.
Also, a red laser beam emitted from a second light source 207 for performing either the recording action or the playback action on the DVD is of polarized laser beam B. The red laser beam emitted from the light source 207 is converted into a collimated light beam by a collimator lens 206. The collimated laser beam is reflected by the dichroic mirror 205 and the polarizing beam splitter 213, passed through the ¼ waveplate 210, and focused by the second objective lens 209 to form its spot on the information recording surface of the DVD.
The laser beam reflected on the information recording surface of the DVD is passed again through the second objective lens 209, converted into the polarized laser beam A by the ¼ waveplate 210, passed through the polarizing beam splitter 213, and projected on the optical detector 215 by the detecting part 214.
As described, the conventional optical pickup 250 is capable of performing either the recording action or the playback action on different types of the optical disc.